Tin (Sn) undergoes a reversible electrochemical alloying reaction with lithium and offers a high theoretical capacity of 993 mA h g−1 or 7313 mA h cm−3. Based on this property this material has the potential of replacing conventional graphite (372 mA h g−1 or 833 mA h cm−3) for negative electrodes in high energy, volume efficient lithium ion batteries. See, for example, Winter, M. et al. Electrochim. Acta 1999, 45, 31-50; Derrien, G. et al., Adv. Mater. 2007, 19, 2336-2340; and Obrovac, M. N. et al., J. Electrochem. Soc. 2007, 154, A849-A855, each of which is incorporated herein by reference in its entirety. However, the electrode undergoes unfavorable structural deterioration due to a huge volume variation between tin and lithium/tin alloy(s). As a result, the cycle life is unacceptable to be used in the lithium ion batteries.
One promising solution to overcome an unacceptable volume variation between tin and lithium/tin alloy(s) that can still take advantage of Sn-based materials for high performance electrodes is to introduce a second metal element (M) to form a tin (Sn) intermetallic compound. (See Mao, O. et al., J. Electrochem. Soc. 1999, 146, 414-422; Kepler, K. D. et al., Electrochem. Solid-State Lett. 1999, 2, 307-309; Tarascon, J. M. and Armand, M. Nature 2001, 414, 359-367; Hassoun, J. et al., Adv. Mater. 2007, 19, 1632-1635; Fan, Q. et al., Electrochem. Solid-State Lett. 2007, 10, A274-A278; each of which is incorporated herein by reference in its entirety.) The second metal, M, buffers the volume change by forming a soft framework, stabilizes the integration of single intermetallic particle, and enhances the electronic conductivity during cycling, and therefore improves the cell's performance regardless of whether M is electrochemically inactive or electrochemically active.
Electrochemically inactive intermetallic Sn-based compounds include Cu6Sn5 (Vaughey, J. T. et al. Electrochem. Solid-State Lett. 2007, 10, A220-A224, incorporated herein by reference in its entirety), CoSn3 (Alcantara, R. et al., Electrochem. Solid-State Lett. 2008, 11, A209-A213, incorporated herein by reference in its entirety), Ni3Sn4 (Hassoun, J. et al., 2007), FeSn2 (Zhang, C. Q. et al. Alloys Compd. 2008, 457, 81-85, incorporated herein by reference in its entirety), MnSn2 (Beaulieu, L. Y. et al. J. Electrochem. Soc. 2000, 147, 3237-3241, incorporated herein by reference in its entirety), CeSn3 (Sakaguchi, H. et al. J. Power Sources 2003, 119, 50-55), CrSn2 (Xue, M. Z. et al. Solid State Ionics 2006, 177, 1501-1507, incorporated herein by reference in its entirety), and LaSn3 (Vaughey, J. T. et al. J. Electrochem. Soc. 2009, 156, A536-A540, incorporated herein by reference in its entirety).
Electrochemically active intermetallic Sn-based compounds include SbSn (Wang, Y. et al. Angew. Chem., Int. Ed. 2006, 45, 7039-7042, incorporated herein by reference in its entirety), Ag3Sn (Wang, X. Y. et al. J. Power Sources 2008, 184, 508-512, incorporated herein by reference in its entirety), and Mg2Sn (Larcher, D. et al. Chem. Mater. 2004, 16, 5502-5511, incorporated herein by reference in its entirety).
Despite the availability of various intermetallic compounds, there is still a need for intermetallic Sn-based compounds that overcome an unacceptable volume variation between tin and lithium/tin alloy(s) by forming a soft framework, by stabilizing the integration of single intermetallic particles, and by enhancing the electronic conductivity during cycling, yet that still avoid significant suppression of the theoretical capacity of pure tin (Sn), which is 993 mA h g−1. For example, while FeSn2 has been identified as the best composition among M-Sn (M=Fe, Cu, Co, Ni) nanospheres (Wang, X-L et al. ACS Appl. Mater. Interfaces 2010, 2, 1548-1551), the presence of Li-storage-inactive Fe in FeSn2 suppresses the theoretical capacity of pure Sn by about 189 mA h g−1 (to 804 mA h g−1). Thus, it is desirable to have a tin-based intermetallic compound with the improved theoretical capacity that can match as close as possible to the theoretical capacity of pure tin (Sn).